Relatively inexpensive and reusable electrical energy storage devices are clearly desirable. Prior art storage devices mainly consist of electrochemical cells. Typical electrochemical cells or batteries, such as iron-nickel and nickel-cadmium cells, have a number of well known disadvantages. Generally, the substances used to produce such cells are expensive and relatively scarce. These substances also tend to be non-recyclable, and potentially harmful to the environment, resulting in both costly production, reclamation and disposal. Electrochemical cells have a limited service life, ie. number of charge/discharge cycles, and shelf life, due to the irreversible reaction of either the electrolyte or electrodes in every charge/discharge cycle. In addition, their efficiency is relatively low, typically in the range of 15–50%, and depends on the operating conditions in which they are used, such as the ambient temperature.
Some advances have been made in the field of electrochemical batteries, such as the suppression of gas evolution by adding variable valency compounds to the electrolyte, and replacing environmentally harmful substances with metal hydrides. However, these advances add considerably to the cost of producing batteries and have not been widely adopted. Furthermore, the primary disadvantages of conventional batteries, there low efficiency, limited lifespan and degrading output, are not greatly improved by these changes.
Capacitors capable of storing large amounts of electrical energy, such as carbon double layer capacitors, are also known. Typically, these capacitors use carbonised materials to form polarized electrodes. Generally, the carbonised material is a paste formed from a carbon particle powder in combination with a binding agent. The carbon paste is spread over a metallic mesh which is packaged in a housing at high pressure to form the electrodes. While such capacitors have a theoretically high capacitance, the paste used exhibits non-Newtonian flow characteristics, and, therefore, under the high pressures required to achieve good electrical properties, the symmetric geometry of the electrodes necessary to produce high capacitance is compromised. Changes in the electrode geometry lead to variations in the electric characteristics of separate cells, which fact leads to the destabilization of the capacitor in general and its eventual breakdown.
It is, therefore, desirable to provide a high capacitance energy storage device that obviates or mitigates at least one of the disadvantages of the prior art.